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October 2002

Copyright © Intel Corporation 2002. *Third-party brands and names are the property of their respective owners. 1

DeveloperUPDATEMagazineIntel

®

GPRS—How Does It Work and How Good Is It?

Nikhil M. Deshpande, Ph.D.

Technical Marketing ManagerEmerging Platforms Lab

Intel Corporation

Jay GilbertSr. Technical Marketing Engineer

Emerging Platforms LabIntel Corporation



October 2002



®

GPRS—How Does It Work and How Good Is It?Nikhil M. Deshpande, Ph.D.Technical Marketing ManagerEmerging Platforms LabIntel Corporation

Jay GilbertSr. Technical Marketing EngineerEmerging Platforms LabIntel Corporation

Overview GPRS (general packet radio service) is a new nonvoice service that is being added to existing IS-136 TDMA (time

division multiple access) networks in the United States and GSM (Global System for Mobile Communications)

networks in the United States and Europe. It provides for the transmission of IP packets over existing cellular networks,

bringing the Internet to the mobile phone. Anything the Internet offers, from Web browsing to chat and e-mail, will be

available from GSM and TDMA service providers via GPRS-enabled devices.

How Does it Work? GPRS is implemented as a 2.5G technology upgrade in the form of a network overlay to existing cellular networks.

Without requiring the dedication of any new channels, GPRS takes advantage of the short bursty nature of IP packet

transmission and effectively grabs short time slots allocated from channels dedicated to voice traffic. Network efficiency

is thus improved, because existing channels already used for voice can be simultaneously used to send IP packets as

well. In addition, most data sessions do not involve continuous data transmission. One user may be transmitting or

receiving while another user is reading information just downloaded. This channel-sharing with other data and voice

users is far more efficient than 2G circuit-switched data services, in which one user locks up an entire channel whether

they are currently transmitting or not.

Each dedicated channel is divided into eight time slots, with each time slot supporting a maximum data transmission

speed of 13.4 Kbps**. In practice, one of these time slots is reserved for control. While it is possible that in special

situations a service operator may choose to allocate the remaining seven time slots to GPRS traffic, the normal

allocation reserves two of these time slots for voice traffic. Because Internet access is generally asymmetric (the user

spends more time receiving data than transmitting data), the remaining five time slots available for GPRS traffic are

allocated in an asymmetric manner as shown, depending on the type of mobile phones being supported:

• Type 2+1—two time slots for download, one for upload

• Type 3+1—three time slots for download, one for upload

• Type 4+1—four time slots for download, one for upload

In addition, GPRS phones are classified as to their ability to support simultaneous GSM voice calls and GPRS data

transmission as follows:

• Class A—capable of simultaneous voice and data transmission

•

Class B—automatic switching (according to phone settings) between voice and data• Class C—hand-operated switching between voice and data

What Does it Promise? The theoretical maximum GPRS data rate is 171.2 Kbps per channel. However, the user will not experience anything

close to this because this data rate assumes no error correction and the use of all eight time slots. Normal data

transmission utilizes error correction, which limits the data rate per time slot to 13.4 Kbps. In addition, because not all

eight time slots are available for GPRS data, the maximum data rate which the user can expect from a service operator

today is 53.6 Kbps (4 time slots x 13.4 Kbps), using a phone that supports Type 4+1 service.



October 2002



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Data rates aside, it does promise an "always on" connection to the Internet, and that is a big upgrade for a network that

previously only provided voice traffic.

How Is it Used? There are two different ways to utilize GPRS to access the Internet (Figure 1). One is to use a GPRS device as a modem

to allow a laptop running a browser to access HTML Web pages. Any Web page that can be accessed from a desktop

browser can now be accessed with a laptop via a GPRS modem.

The second method is to connect to the Internet directly with the mobile GPRS device and use a built-in microbrowser

to access WAP (wireless application protocol)-enabled Web pages. WAP content is restricted to text only and thus

requires far less bandwidth to load. Microbrowsers cannot read, and are prevented by the switching network from

attempting to access any Web pages that do not contain WAP content. Because typing in URLs can be tedious on a

mobile phone with limited space for a keyboard, service providers often allow the user to customize a WAP portal. This

provides quick and easy access, with a minimum of button-pushing, to a small number of WAP-enabled sites selected by

the user.

Figure 1. Different configurations for utilizing GPRS to access the Internet.

WWANBase Station

Switching

Network

BluetoothLink

GPRSLinks

Cellphoneas GPRSModem

SerialLink


Internet

PCMCIA asGPRS modem


Cellphoneas Stand-aloneMicrobrowser

IrDA Link

How Good Is GPRS? Because some are making lofty claims for GPRS ease-of-use and bandwidth, the Intel Research and Development

network set out to discover what users can actually expect from this new service. Experiments were conducted using a

variety of equipment configurations, under different conditions, and in a number of cities. For specific information about

the tests, including performance results and what we learned about roaming and billing, please read the white paper

linked to in the More Info section.



October 2002



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All in all, we found that GPRS performance is comparable to a 56-Kbps dial-up service. Depending on the user's

expectations, this can be viewed as much more than was previously available or not what the user had hoped for.

Certainly, rates over 100 Kbps are not realistic, but the advertised rate of 53.6 Kbps for 4+1 service is. Users used to

dial-up speeds will be pleased to find they can get as good or better bandwidth by using their cell phone as a modem

while on the road.

It also bears remembering that the service is new. As more subscribers sign up for GPRS service, bandwidth will tend todrop. Service providers will add capacity to meet users' needs, either in the form of allocating more time slots per

channel, building more capacity in the form of additional cell towers, or incorporating smart antenna technology to

increase network efficiency.

Summary As an interim step from 2G to 3G technology, GPRS goes a long way toward introducing the user to wireless data

services. While the data rates do not approach those promised by future 3G technology, GPRS will nonetheless serve as

a spawning and proving ground for new services and applications that take advantage of wireless data transmission.

This, in turn, will help generate new revenue that is needed by service providers to help pay for 3G infrastructure and

spectrum.

More Info Read the full white paper from which this GPRS article is derived, which discusses the specifics of the tests more indepth. Or, you can find more information about how the Intel R&D network is Building the Wireless Tomorrow.

Author Bios Dr. Nikhil Deshpande is technical marketing manager in the Mobile Service Technologies group of the Emerging

Platforms Lab, part of the Corporate Technology Group. He is currently responsible for the technology marketing of

various wireless technologies, enabling innovative services for mobile operators. Deshpande has been at Intel for two

years. Prior to coming to Intel, he worked at Tektronix Inc. on a variety of wireless technologies. He has been awarded

three patents, and has six patents pending on digital communications and wireless technologies, as well as eight patents

pending in the field of communications systems. Deshpande holds a B.S.E.E. degree from the University of Poona,

India, as well as M.S. and Ph.D. degrees in electrical and computer engineering from Portland State University.

Jay Gilbert is a senior technical marketing engineer in Intel's Emerging Platforms Lab within the Corporate Technology

Group (CTG). He is responsible for standards development and new form-factor mobile platform efforts within CTG, as

well as technical evangelism within the communications industry for several multimedia products. Gilbert has been with

Intel for more than 11 years. Prior to his current position, he worked at Development Tools Technical Marketing and as

a product marketing engineer for ProShare®

Video conferencing products. Gilbert has a B.S.E.E. from the Oregon

Institute of Technology, and an M.B.A. from Portland State University.

** "GPRS Technology", Intel Corporation, 2002.

—End of Intel Developer Update Magazine Article—

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